Pile or caisson supported foundations have been used commonly for construction on loose or unstable soils, sinking soils, hillsides, cliffsides, seasides and earthquake zones. Loss of soil support at the base of the caisson can occur with soil erosion in most areas, and with soil liquefaction in earthquakes. Pile design practice is based on preventing or mitigating a bending mechanism, wherein lateral loading due to soil loss, movement or spreading induces bending failure in the pile. Less common are considerations necessary to avoid buckling of a pile due to axial load acting on it during a soil liquefaction event.
Gravel and stone can be added to the bottom of a hole dug for a foundation piling to allow rainwater to drain through around the piling base, but this merely underlines the existence of expansive and collapsible soils at the base of many foundation pilings. Where bedrock cannot be reached, the piling relies on upward forces from side friction with the soil and the relatively narrow contact between piling base and soil at the depth of the base, which can be expected to contract and expand.
Preparing the foundation piling hole at depth with soil and gravel can slow or mitigate soil settling and water movement, but cannot truly prevent them. What is sought, then, is a method and apparatus that acknowledges the problems of water and soil movement at the base of a foundation piling or caisson and incorporates structures to take advantage of said water and soil movement in ways that improve stability of the piling at depth. Specifically, such a structure would passively use rain or ground water movement to expand into compressed or vacated soil at depth. It would passively use soil movement to solidify this expanded structure. It would incorporate sensors for monitoring the soil conditions at depth. And, it would allow for active addition of concrete material at depth in instances where soil sensors indicated that passive measures were insufficient.